Low Stress Threadform with a Non-conic Section Curve
In one aspect of the present invention a threadform has a load bearing flank and a non-load bearing flank joined by a thread root. The load bearing flank tangentially joins the thread root at a first angle, and the non-load bearing flank joins the root to a second angle. The root is made of a single non-conic section curve.
This application is a continuation in part of U.S. patent application Ser. No. 11/947,949. This application is also a continuation in-part of U.S. patent application Ser. No. 11/841,101, which is a continuation in part of U.S. patent application Ser. No. 11/688,952. The abovementioned references are herein incorporated by reference for all that they contain.
BACKGROUND OF THE INVENTIONThe present invention relates to threadforms. Highly loaded threadforms often fail from fatigue with cracks initiating at the thread root. Most prior art threads include thread roots with radii of curvature, generally believing that a larger radius of curvature will yield a lower stress threadform. However, the prior art does include several references teaching that thread root curves defined by a portion of an ellipse advantages have over root threads formed by radii as taught in U.S. Pat. Nos. 4,799,844 to Chuang; 5,056,661 to Yousef, 5,060,740 to Yousef, 5,163,523 to Yousef, 5,544,993 to Harle; 5,736,658 to Harle; 7,210,710 to Williamson; and U.S. Patent Publication No. 2005/0189147 to Williamson. All of these references are herein incorporated by reference for all that they contain.
Both circles and ellipses are conic sections, meaning that they comprise a closed curvature defined by the intersection of a plane with a cone. In threadform prior art, curves are described as being defined by a portion of either a circle or an ellipse. Those threadforms defined by a portion of a circle have a constant radius of curvature.
BRIEF SUMMARY OF THE INVENTIONIn one aspect of the present invention a threadform has a load bearing flank and a non-load bearing flank joined by a thread root. The load bearing flank tangentially joins the thread root at a first angle, and the non-load bearing flank joins the root to a second angle. The root is made of a single non-conic curve. The sharpest section of the curve may be between a midpoint of the curve and the load bearing flank. The curve may have a constantly changing radius of curvature.
The first and second angles may be 55 to 65 degrees. In some embodiments, the threadform is an internal threadform or an external threadform and may be tapered.
In another aspect of the present invention, a threadform is formed on a tool string component. A load bearing flank and a non-load bearing flank are joined by a thread root. The load bearing flank tangentially joins the thread root at a first angle of 55 to 65 degrees and the non-load bearing flank joins the root at a second angle of less than 55 to 65 degrees. The root also has a single non-conic curve. The threadform may formed proximate an end of the tool string component or formed in between tool joints connected to ends of the tool string component.
The individual sleeves 203 may allow for better axial and torsional flexibility of the component 200 than if the component 200 comprised a single sleeve spanning the pockets 201. However, in some embodiments of the present invention, a single sleeve is used. The sleeves 203 may also comprise a plurality of grooves adapted to allow the sleeves 203 to stretch and/or flex with the tubular body 205. At least one sleeve may be made of a nonmagnetic material, which may be useful in embodiments using magnetic sensors or other electronics. The pockets 201 may be sealed, though a sleeve and the pocket may comprise openings adapted to allow fluid to pass through the sleeve such that one of the pockets is a wet pocket.
Electronic equipment may be disposed within at least one of the pockets of the tool string component. The electronics may be in electrical communication with the aforementioned telemetry system, or they may be part of a closed-loop system downhole. An electronics housing 216 may be disposed within at least one of the pockets wherein the electronic equipment may be disposed, which may protect the equipment from downhole conditions. The electronics may comprise sensors for monitoring downhole conditions. The sensors may include pressure sensors, strain sensors, flow sensors, acoustic sensors, temperature sensors, torque sensors, position sensors, vibration sensors, geophones, hydrophones, electrical potential sensors, nuclear sensors, or any combination thereof. Information gathered from the sensors may be used either by an operator at the surface or by the closed-loop system downhole for modifications during the drilling process. If electronics are disposed in more than one pocket, the pockets may be in electrical communication, which may be through an electrically conductive conduit disposed within the flange separating them.
The shoulders formed by collars 300 and 400 may place the sleeves or sleeve, depending on the embodiment, in compression. In some embodiments, this compression may be enough to support the assembly in torsional and axial forces with the help of pins or fasteners.
Referring now to
The component 200 may be assembled at the drill site. The first shoulder collar 300 may be keyed to the component by a plurality of pins 305. The left-threaded collar 303 may be disposed around the component before the first shoulder collar 300 during assembly. After the left-threaded collar 303 is threaded on the component, the first shoulder collar 300 may then be slid into position from the opposite end of the component 200 over the plurality of pins 305 which keys the component to the component.
The flanges 202 may then be placed around the component, with the first flange 208 being keyed to the primary shoulder 301, possibly by another plurality of pins 320, in order to keep the first flange 208 rotationally stationary and provide torsional support. The flanges 202 may comprise O-rings 306 disposed around an outer diameter 307 of the flanges and/or within an inner diameter 308 of the flanges 202, such that the pockets 201 may be sealed when the sleeves 203 are placed around the component. The first sleeve 207 may abut a portion of the primary shoulder 301.
The component may also be pre-assembled prior to shipping to the drill site. In such embodiments, the sleeves may be press fit around the flanges. A grit may be placed into the press fit such that the grit may gall the surfaces of the flange and sleeve in order to create more friction between the two surfaces, wherein a stronger connection is made.
Referring now to
The thread root comprises a curve 610 defined by a non-conic section The curve has a constantly changing radius through out its length. The curve is sharpest between a midpoint 609 of the length of the curve and load bearing flank. Unlike a curve defined by an ellipse or circle, if curve 610 were to continue beyond the flanks, it would not produce a symmetric closed curve.
Unlike the teachings of U.S. Pat. No. 4,799,844; column 2, lines 23-30 and column 4, lines 34-68, where a larger radius of curvature is preferred for the deepest portion of a thread root, curve 610 comprises its sharpest portion at the deepest portion of the thread root. The radii of curvature increase towards the load bearing flank and the non-load bearing flank differently from the midpoint. From the midpoint the radii of curvature increase gradually towards the non-load bearing flank. From the midpoint to the load bearing flank, the radii of curvature decrease rapidly, then increase rapidly, followed by a gradual increase along the length of the curve.
Threadform 608 surprisingly yields a superior gradation of strain compared to conic transitions with resulting lower stress at the root of the thread over similar prior art threads.
Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.
Claims
1. A threadform, comprising:
- a load bearing flank and a non-load bearing flank joined by a thread root;
- the load bearing flank joins the thread root at a first angle and the non-load bearing flank joins the root to a second angle; and
- the root comprising a single non-conic section curve.
2. The threadform of claim 1, wherein a sharpest section of the curve is between a midpoint of the curve and the load bearing flank.
3. The threadform of claim 1, wherein the curve comprises a constantly changing radius of curvature.
4. The threadform of claim 1, wherein the first angle is 55 to 65 degrees.
5. The threadform of claim 1, wherein the non-load bearing flank joins the root tangentially.
6. The threadform of claim 1, wherein the second angle is 55 to 65 degrees.
7. The threadform of claim 1, wherein the threadform is an internal or external thread form.
8. The threadform of claim 1, wherein the threadform is tapered.
9. The threadform of claim 1, wherein a sharpest portion of the thread root is a deepest portion of the root thread.
10. The threadform of claim 1, wherein the loading flanks tangentially joins the thread root.
11. A threadform formed on tool string component, comprising:
- a load bearing flank and a non-load bearing flank joined by a thread root;
- the load bearing flank tangentially joins the thread root at a first angle of 55 to 65 degrees and the non-load bearing flank joins the root at a second angle of less than 55 to 65 degrees; and
- the root comprising an single non-conic curve.
12. The threadform of claim 11, wherein the threadform is formed proximate an end of the tool string component.
13. The threadform of claim 11, wherein the threadform is formed in between tool joints connected to ends of the tool string component.
14. The threadform of claim 11, wherein a sharpest section of the curve is between a midpoint of the curve and the load bearing flank.
15. The threadform of claim 11, wherein a sharpest portion of the thread root is a deepest portion of the root thread.
16. A threadform, comprising:
- a load bearing flank and a non-load bearing flank joined by a thread root;
- the load bearing flank joins the thread root at a first angle and the non-load bearing flank joins the root to a second angle; and
- the root comprising at least one non-conic section curve.
17. The threadform of claim 16, wherein the threadform is a semi-buttressed threadform.
18. The threadform of claim 16, wherein the threadform is a tapered threadform.
19. The threadform of claim 16, wherein a sharpest portion of the thread root is a deepest portion of the root thread.
20. The threadform of claim 16, wherein at least two non-conic section curves are separated by a flat.
Type: Application
Filed: Oct 7, 2009
Publication Date: Jan 28, 2010
Inventors: David R. Hall (Provo, UT), Scott Dahlgren (Alpine, UT)
Application Number: 12/575,237
International Classification: E21B 17/042 (20060101); F16B 7/18 (20060101); F16L 15/06 (20060101);